1. Field of the Invention
The invention relates to a semiconductor device, and in particular to a semiconductor memory device and a fabrication method therefor.
2. Background of the Related Art
In fabricating a related semiconductor memory device, higher integration requires shortening of the length of a MOSFET device channel therein. Therefore, when a high voltage is applied to a drain region of the MOSFET, a short channel may give rise to a punch-through defect. In order to overcome such a disadvantage, a halo ion implanting process, which involves implanting a p-type impurity into a semiconductor substrate inside a lightly doped drain (LDD) region, has been developed in an n-channel transistor.
A fabrication method of a related semiconductor device will now be described with reference to FIGS. 1A to 1C.
Referring to FIG. 1A, a gate oxide film 101 and a gate electrode 102 are formed atop a p type semiconductor substrate 100.
Thereafter, as shown in FIG. 1B, halo ion implanting layers 103 are formed by implanting boron ions below the gate electrode by performing a large angle tilt ion implantation process at approximately 25 to 30 degrees. The pocket impurity layers 103 are formed to be more highly doped than the semiconductor substrate 100. Lightly doped impurity layers 104 called lightly doped drains (LDD) are formed by using the gate electrode 102 as a mask and by implanting an impurity such as, for example, As or P ions into the p type semiconductor substrate 100.
As illustrated in FIG. 1C, an insulation film is formed on the resultant structure of FIG. 1B. An anisotropic etching is carried out thereon, and thus sidewall spacers 105 ions are formed at the sides of the gate electrode 102. Source/drain regions 106 are formed by using the sidewall spacers 105 as a mask and by implanting, for example, AS or P ions into the semiconductor substrate at a high doping degree.
As a result, the impurity of an opposite conductive type to the source/drain regions forming the halo ion implanting layer is implanted around the LDDs at a high doping degree, and thus a depletion layer in a drain region is not expanded into a source region, thereby preventing the punch through effect.
However, the conventional semiconductor device has various disadvantages. For example, that the halo ion implanting layer is more highly doped than the semiconductor substrate, and thus an electric field of the source/drain region is increased, which results in a hot carrier effect. Accordingly, it weakens reliability of the semiconductor device. In addition, the junction capacitance is increased by the halo ion implanting layer, and thus an operational speed of the semiconductor device is reduced.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the various disadvantages of the background art and provide at least the advantages described below.
An object of the invention is to prevent a punch-through defect.
Another object of the invention to provide a semiconductor device and a fabrication method therefor in which an oxide film is formed around a source/drain region, instead of forming a halo ion implanting layer as in the related art.
In order to achieve the above-described object of the invention, there is provided a semiconductor device including: a semiconductor substrate; a gate oxide film formed on the semiconductor substrate; a gate electrode formed on the gate oxide film; trenches formed in the semiconductor substrate on the both sides of the gate electrode; an oxide spacer formed at a bottom corner of each trench; and a conductive material formed on each oxide spacer, and filling up each trench.
There is additionally provided a semiconductor device comprising a semiconductor substrate and a transistor formed on the substrate. The transistor comprises first and second trenches, an oxide spacer formed at a bottom inside corner of each the first and second trenches and a first conductive material formed at an upper portion of each oxide spacer and filling up each of the first and second trenches. The conductive material filling up each of the first and second trenches is preferably a doped polysilicon or a doped monocrystalline silicon formed by an epitaxial growth process. The device may further comprise a gate oxide film formed on the semiconductor substrate and a gate electrode formed on the gate oxide film with the first and second trenches formed respectively on each side of the gate electrode. An insulating sidewall spacer may be formed at each sidewall of the gate electrode, and an impurity layer may be formed in the semiconductor substrate below each sidewall spacer. Further, the conductive material in each of the first and second trenches may be operated as a source or drain of the transistor, respectively.
There is also provided a method for fabricating a semiconductor device including: forming a gate oxide film and a gate electrode on a semiconductor substrate; forming an impurity layer by implanting impurity ions into the semiconductor substrate on both sides of the gate electrode; forming a sidewall spacer at the sidewall of the gate electrode; forming trenches in the semiconductor substrate at the outer sides of both the sidewall spacers; forming an oxide spacer at a bottom corner of each trench; and filling up each trench with a conductive material.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.